PROMISSORY NOTE

Exhibit 10.1

PROMISSORY NOTE

References in the boxes above are for Lender’s use only and do not limit the applicability of this document to any particular loan or item.  Any item above containing “***” has been omitted due to text length limitations.

PROMISE TO PAY. TGC Industries, Inc. (“Borrower”) promises to pay to Sovereign Bank (“Lender”), or order, in lawful money of the United States of America, the principal amount of Five Million & 00/100 Dollars ($5,000,000.00) or so much as may be outstanding, together with interest on the unpaid outstanding principal balance of each advance. Interest shall be calculated from the date of each advance until repayment of each advance or maturity, whichever occurs first.

CHOICE OF USURY CEILING AND INTEREST RATE. The interest rate on this Note has been implemented under the “Weekly Ceiling” as referred to in Sections 303.002 and 303.003 of the Texas Finance Code. The terms, including the rate, or index, formula, or provision of law used to compute the rate on the Note, will be subject to revision as to current and future balances, from time to time by notice from Lender in compliance with Section 303.103 of the Texas Finance Code.

PAYMENT. Borrower will pay this loan in one payment of all outstanding principal plus all accrued unpaid interest on September 16, 2009. In addition, Borrower will pay regular monthly payments of all accrued unpaid interest due as of each payment date, beginning October 16, 2008, with all subsequent interest payments to be due on the same day of each month after that. Unless otherwise agreed or required by applicable law, payments will be applied first to any accrued unpaid interest; and then to principal.  Borrower will pay Lender at Lender’s address shown above or at such other place as Lender may designate in writing.

VARIABLE INTEREST RATE . The interest rate on this Note is subject to change from time to time based on changes in an independent index which is the Wall Street Journal Prime as quoted in the Southwestern Addition of Wall Street Journal the “Index”). The Index is not necessarily the lowest rate charged by Lender on its loans. If the Index becomes unavailable during the term of this loan, Lender may designate a substitute index after notifying Borrower. Lender will tell Borrower the current Index rate upon Borrower’s request. The interest rate change will not occur more often than each day. Borrower understands that Lender may make loans based on other rates as well. The Index currently is 5.000% per annum.  The interest rate to be applied prior to maturity to the unpaid principal balance during this Note will be calculated as described in the “INTEREST CALCULATION METHOD” paragraph using a rate equal to the index, resulting in an initial rate of 5.000% per annum based on a year of 360 days.   NOTICE: Under no circumstances will the interest rate on this Note be more than the maximum rate allowed by applicable law. For purposes of this Note, the “maximum rate allowed by applicable law” means the greater of (A) the maximum rate of interest permitted under federal or other law applicable to the indebtedness evidenced by this Note, or (B) the “Weekly Ceiling” as referred to in Sections 303.002 and 303.003 of the Texas Finance Code.

INTEREST CALCULATION METHOD.  Interest on this note is computed on a 365/360 basis; that is, by applying the ratio of the interest rate over a year of 360 days, multiplied by the outstanding principal balance, multiplied by the actual number of days the principal balance is outstanding, unless such calculation would result in a usurious rate, in which case interest shall be calculated on a per diem basis of a year of 365 or 366 days, as the case may be.  All interest payable under this Note is computed using this method.

PREPAYMENT. Borrower may pay without penalty all or a portion of the amount owed earlier than it is due. Prepayment in full shall consist of payment of the remaining unpaid principal balance together with all accrued and unpaid interest and all other amounts, costs and expenses for which Borrower is responsible under this Note or any other agreement with Lender pertaining to this loan, and in no event will Borrower ever be required to pay any unearned interest. Early payments will not, unless agreed to by Lender in writing, relieve Borrower of Borrower’s obligation to continue to make payments of accrued unpaid interest. Rather, early payments will reduce the principal balance due. Borrower agrees not to send Lender payments marked “paid in full”, “without recourse”, or similar language. If Borrower sends such a payment, Lender may accept it without losing any of Lender’s rights under this Note, and Borrower will remain obligated to pay any further amount owed to Lender. All written